Electromagnet



Feb. 23, 1932. M. LAVET 1,847,012

ELECTROMAGNET Filed Oct. 13, 1930 2 Sheet-Sheet l Feb. 23, 1932. M.LAVET 1,847,012

ELECTROMAGNET Filed 001;. 13, 1930 2 Sheets-Sheet 2 mum 72 wwia PatentedFeb. 23, 1932 UNITED STATES PATENT OFFICEv name LAVE'I', OI PARIS,FRANCE, ASSIGNOR '10 ETABLISSEHENTS L'EON EATOT, OI PARIS, FRANCE, ACORPORATION OF FRANCE mac-momentum Application fled October 18, 1980,Serial No. 488,502, and in France (lotober 17,

The presentinvention relates'to improvements in electro-magnets(associated or not with electric contacts) and to their application toelectric clocks and watches whether self-contained or 0 rated from adistance, provided or not witli triking movements and chimes, andtovarious other apparatus such as chimes, vibrators, electric twmklers,polarized relays, battery charges, synchronous motors, contactlessrotating motors, loud speaker motors, pick u s, etc.

In the industries o electric clocks, telegraphy and wireless, electro-maets are employed in many apparatuses w ich have an alternating movement,these being 'rincipall employed for operating ban 5, for win ing upsprings, for operating electric contacts, etc.

The requirements for electro-magnets are generally as follows:

1. Good electric efliciency, and small inherent resistances, the latterarising principally from sticking and magnetic attractions from inertiaof the parts to be displaced and 5 from mechanical friction.

2. Simple construction and low cost of manufacture.

3. Small weight and reduced overall dimensions of the electro-magnet andreduced consumption, specially for portable time instruments such asclocks etc. and for time receivers disposed in the centre of translucentdials.

4. In several applications, good electrical efficiency must be obtainedfor a very low supply voltage.

This last quality is in articular sought for electric watches and c ockswhich must operate by means of a battery of small size lasting for avery lon time.

In order that the asting power shall be good (for example exceeding twoyears), it is found that it is advantageous, for given overalldimensions, to use a battery of a single element (1', 5) rather thanbatteries of three elements (4", 5) like the batteries for pocket lamps.For the same consumption in watt hours, with a very slow rate ofdischarge, the duration is better. Calculation and experience show thatpolarized electro-magnets .are found,

automobile watches and give the best results for utilizing the ener ofthe battery in question than ordinary s3 iron electro-magnets. In allcases, the polarized electro-magnet systems employed hitherto, arebulky, heavy, and costly. Further they comprise strong magnets whichgive rise to considerable friction and ma etic sticking. This is alsocaused b the act that the conception of the shapes 0 their variousconstituent parts does not permit easy assurance of the equality of thewidths of air ap, and that in practice relatively large di erencesproducing lack of balance of the magnetic forces and much reducing theefiiciency particularly when it is a question of producing a relativelysmall mechanical power, as is the case for the application contemplated.

The present invention relates in the first place to improvements in verysmall polarized electro-magnets capable of bein housed in the casings oflarge watches, suc as automobile watches.

The details of construction and the shapes of the constituent partsenable all the members to. be collected into a very restricted space,and permit the maximum use of first class materials in order to obtain avery high electric power of the apparatus.

To obtain this last result, the actual state of the art shows that it isadvantageous to employ:

1. A magnet of steel or cobalt such that the ratio between the lengthand the other dimensions is preferably less than in magnets ofhorse-shoe type.

2. For the iron parts magnetized by the winding, silicon sheet metal, orelectrolytic iron, or any other product having great permeability andvery small hysteresis (esgecially certain ferro-nickel alloys when theeld is weak).

3. A winding of high conductivity copper with spires of as small alength as possible disposed to accommodate the maximum volume of copper.

4. Air gaps of large surface and small thickness permittin variation ofthe reluctance of the de ormable' magnetic cirin relation to the weightexplosion motors.

cuits within ve wide limits according to a predetermin law dependentupon the applications.

he magnetic products in questionabovc are very costl and further areonly commercial y pro table in certain forms (especially cylindricalrods and thin plates).

The invention enables these materials to be used in most favourableconditions and it equally concerns various devices and applications ofthese systems associated with special electric contacts.

The object of the invention is set out in the followin structional ormsw ich have been illustrated by way of example in the attached drawin Ont e drawings: Y

Figure 1 shows the usual method of constructing magneto-electricmachines ac-' tually known.

Figures 2, 3 and 4 show in projection with parts in section, a polarizedelectro-magnet provided with improvements constituting the object of theinvention.

Figures 5, 6 and 7 are detail views of the constituent members of theelectro-magnet.

Figures 8, 9 and 10 are diagrammatic figures showing the effect of theshape of the pole pieces of the movable armature of theelectro-magnet.

Figures 11 and llbis show a modification of the arrangement of themagnet.

Fi ure 12 shows diagrammatically the apphcation of theelectro-magnetassociated with an electric contact in an electricallywound clock or watch.

Figure 13 is a dia am of the electric circuit of the system s own inFigure 12.

Figure 14 shows separately the electric contactwhose closure isautomatically produced. 7

Figures 15 and 16 show the application of the invention to timereceivers operating by means of alternating emissions of the electriccurrent.

The improvements forming the object of the invention relate moreparticularly to the known t pe of polarized electro-magnet shown inigure 1. This ty e of electro-magnet comprises a magnet provided withheavy polar expansions A an A and a coil wound on an iron armature Brotating about the axis C. The coil is well known under the name ofSiemens shuttle. This system is emplo ed as a motor, or as a currentgenerator. n this last application, it is employed very frequently as teignition magneto for Practice shows that the electro-magnet constructedand proportioned as indicated in Figure 1 does not allow theadvantageous production of sensitive electro-magnets and economicmanufacture suited to electric clockwork and like applications. This isbecause when the movable ardescri tions of various conmature of theapparatus of Figure 1 is rotated, very intense forces of magneticattraction are exerted on this part which tend to rotate the coil incertain directions dependent on the shape ofthe pole pieces. Theseforces exist when the coil is not traversed by the electric current.They also persist when the coil is energized by a current and theyprevent displacement when the current is weak. Displacement is onlyproduced when the current is very intense and, even in this case thedriving cou le obtained is irre ular an the electrical e ciency isimpaired because the value of the current has to be increased in orderthat the apparatus may overcome the inherent resistances for thepositions airresponding to the minimum driving coup e.

These disadvantages are eliminated with the improved method ofconstruction described with reference to Figures 2, 3 and 4.

According to the invention, the electromagnet consists of a magnet A,preferably of steel or cobalt, and a movable coil whose core N is ofelectrolytic iron or like metal whose coeflicient of magneticpermeability is very hi h.

The coi is rovided with polar enlargements B and 2 constructed ofstamped and bent sheet metal. 'The metal constituting them must be ofvery high ma etic permeabilit and very weak hysteresis, (for exiti n le0 silicon sheet or alloy of like properies The shape of the pole piecesis of very great importance, and it may be modified according to theapplications. Generally it is desired that the coil be operated by avery weak current and that the driving couple be of a value which isvery high and constant over considerable angular displacement. Thisresult is obtained with the shapes and proportions shown in thedrawings.

The movable coil pivots in holes cut in the two brass plates C and CThese plates are connected together by four iron pillars P P P and Pwhich constitute the fixed pole pieces of the apparatus. These poles areconnected magnetically to the magnet by the stain ed angle pieces ofsheet iron E and E hese parts E and E are slightly flexible and theybear with heavy pressure on the polar extremities of the magnet and onthe pillars P P P and P The use of the flexible parts E and E has theimportant advantage of permitting very weak reluctance of the joints andstrong magnetization of the pillars to be obtained. This result isobtained without the necessity of having an extremely precise spacing ofthe limbs of the i magnet. The magnets can consequently be less costlythan if it was necessary to grind the magnet to a very exact size. The Ushape of the parts E and E should also be noted.

The parts E and E are shown separately in employed to parts E and E,also enables a sufiiciently Th large free space to be preserved betweenthe magnet and the movable coil. This space is receive the flexiblewires connectin the movable coil with the fixed terminals 0% thecircuit. B bending back these connections on themse ves and by makinthem of considerable length, the fiexure o t e wire is limited to greatflexibility is obtained; also breaka e of the wire in s ite of a largenumber of displacements of the coil is prevented.

The details of construction of the movable coil are shown in the detailviews (Figures 5, 6 and 7). The two pivots O and 0 are riveted on twobrass parts H and H connected together by two pillars D and D The pivotsO and O engage the holes in the lates C and 0,.

e-coil B is wound beforehand on the core which terminates in twothreaded rods on which can screw the nuts G nuts permit the wholeassembly of the constituent parts of the coil (that is to say, the brassparts H and H the pole pieces B and B and the coil B) to beaccomplished. 1'0 this end the outline of the parts H and H, comprisestongues t and shoulders e. The tongues t engage exactly in recesses inthe parts 13 and B and all the parts are maintained firmly in welldefined emplacements and can be fitted up by suitable manipulations. Itshould be understood that certain changes may be made within the spiritof the invention. In particular the nuts G and G may be replaced byscrews screwing into the core N. 7

'It should be noted that this special method of construction has twoparticularly important advantages:

1. The play between the cylindrical pole pieces P P P and P and themovable parts B and B depend only upon these parts being produced bystamping. In effect the pivot hole and the three guide holes for thepillars P P P, and P, can be stamped simultaneously in the parts C and CThe parts B and B are applied by locking of the nuts G and G on theparts H and H obtained by stamping. It is known that the method ofmanufacture by stamping enables very large series of parts which areexactly interchangeable being obtained.

This method of construction will thus permit very great accuracy beingobtained, particularly in re ard to the play or air gap between the po epieces. This is very important, for practice shows that very slightdifferences in the values of the air gaps alter considerably the drivingcouple as well as the value of the magnetic attractions acting on thecoil.

2. The parts constituting the magnetic cirunit are only formed bycylindrical parts of a small value and a cut tapped holes in very thinmetal.

and G These P by very thin sheet metal. e coil support is alsoconstituted by very thin stampings. Consequently the maximum space isthus obtained for receiving the electric windin This is particularlyimportant for the pro uction of very small electro-magnets, for theoryand practice show that one can only obtain good efiiciency on conditionthat the coil is made as long as possible. The out in thin sheet metalare diificult to assemble rigidly for one cannot small diameter or theconstruction shown in 1 sembly is obtained by nuts 1 and G and smallscrew threaded pillars D and D whereby perfect rigidity is obtained,even if the electro-magnet is given very small dimensions.

When the current is interrupted and the coil is rotated by hand, themagnetic attraction due to the magnet A and acting between pole pieces Band B and the iron pillars P P and P varies according to a certain lawwhich depends on the variation of the total reluctance of the magneticcircuit with the angle of rotation. It is well known that in variablemagnetic circuits natural direction of displacement of the movable partis such that it reduces the reluctance of the circuit to a minimum.

In the apparatus shown in Figures 2 to 6, the total reluctance of themagnetic circuit depends mainly on the reluctance of the air gaps, thatis to say, on the air spaces bounded by the adjacent parts of thepillars P P P and P and of the pole pieces B and B When the coilrotates, the reluctance of certain air gaps increases and that of otherair gaps decreases. This variation depends both on the thickness of theair gap and on its area. Compensation for this variation can be obtainedby giving the parts B and B a certain stamped shape and by centeringthese parts either concentrically with the axis of rotation 0 0 or witha certain degree of eccentricity in order to vary the play or air gapwith the angle of rotation.

The shape shown in Figure 6 permits the 0011 provided with ironenlargements B and B to be in neutral equilibrium in the internalmagnetic field produced by the magnet A. his coil may be displaced bymeans of a very weak force. If the coil is brought to any point in itspath it remains in position without having any tendency to return or tocontinue its movement. It should be noted that this result is obtainedby shaping the sides of the pole pieces as arcs of circles m ,-n g and mm, g (Figure 6). Further, the angles m m 9 and 92 are slightly directedtowards-the centre as is indicated in Figure (ibis. The radius of thepoints R is slightly smaller than the radius R of the adjacent part ofthe core of the coil.

These shapes and proportions have been ure 7, the asthe proportionsindicated determined experimentally. For certain applications it isadvantageous to depart from in Figures 6 and (ibis, in order to bringthe coil in certain positions. Figures 8, 9 and 10 indicate by way ofexample the properties of three shapes of the po e pieces B and B If themean are formed by the pole pieces B and B is relatively small inrelation to the distance of P and P as indicated in Figure 8, the meanposition shown on this figure is a position of unstable equilibrium.When the current is stopped, the coil tends to be displaced eithertowards the left or towards the right, so that the pole pieces B and Bcome opposite to the poles P and P..

or the poles P and P If the mean are formed by the pole pieces B and Bis relatively large in relation to the separation between P and P asindicated by Figure 9, the mean position shown on this figure is aposition of stable equilibrum. The coil tends of itself to come betweenthe poles P and P under the influence of the magnetic force ofattraction due to the magnet.

Figure 10 shows such a shape for the pole pieces B and 13 that the coiltends to be displaced in the direction of the arrow f,. It is sufficientto make the curvature of the pole pieces such as B eccentric. Thedisplacement tends to diminish the play with the pillar P or the airgap. This means may be combined with that of giving a certain stampedshape to the pole pieces B and B The outline may be asymetric. Byadopting the proportions of the plan view, Figure 1062's, and by makingIR very slightly less than R the result may be obtained that the coil isbrought back in the direction f with a very small and constant force, as

if adbalanced part returned by a spring were use The magnet A onlyhaving the function of strongly magnetizing the pillars P and P P and Pmay be disposed in different manners. In particular, it may be placed asshown in Figure 11. To obtain a very high driving force with a weakcurrent, it is desirable to increase the magnetic flux of the magnet andto reduce the reluctance of the magnetic circuit. This double result isobtained by the arrangement shown in Figure llbis which is a sectionalview corresponding to Figure 11. It will be seen that two magnets A andA disposed side by side are employed. The length of the pole pieces Band B in the direction parallel to the axis 0 O is increased and thisalso increases the surface of the air gap and enables a much greaterelectromagnetic force to be obtained than if the plates C and C werecloser together, and than if there were only a single magnet employed.

Actually the manufacturers of power electro-magnets adopt similar forms;The apparatuses are produced by preserving the same proportions and byincreasing all the dimensions. Consequently, none of the parts of onemodel can serve in larger models.

This disadvantage may be avoided by adopting the arrangement'of Fi rellbis. For example the small model wil comprise a single magnet, thenext model two magnets, and so on. The whole series can thus be obtainedwith a ve large number of common parts, which is evidently advantageousin the manufacture in series.

The improved electro-magnet that I have 'ust described may be associatedwith a nown electric contact system which closes in the oscillations ofthe coil in a redetermined direction; if the one end 0 the coil isenergized in a suitable direction by this contact, and if the coil isreturned in the direction opposite to the attraction, the coil tendsitself to have a to-and-fro movement. The action is like that ofelectric trembler bells, with the difference that the alternating movingmotor thus produced functions with a much reater efiiciency than that ofhouse bells. he consumption of electricity and the wear of the electriccontact is much less than if an electro-magnet of soft iron wereemployed. The circuit is also much less inductive and there is notendency for the formation of sparks as strong as those which areproduced with the contacts operating non-polarized electro-magnets.

The extent of the displacements can be increased by any known means. Theelectromagnet described in the present description can then be appliedto the production of alternately moving motors for all applications. Wewill confine ourselves to mentioning the following applications:

The electro-magnet can be employed as a I polarized relay for closing acontact. By giving to the pole pieces the shape of Figure 9, threepositions may be obtained; the middle position of rest corresponding tobreakage of the circuit and the extreme positions to right and leftcorresponding to the closure of two distinct contacts.

Employed in an electric bell, the electromagnet may permit extremereduction of the consumption of current. Such a bell is speciallysuitable as an electric clock bell provided with a time contact serving,for example, as a morning alarm. The small battery for operating themovement is sufficient for operating the alarm bell.

In all the known systems for rewinding the weights and driving springsof time mechanisms by means of an electro-magnet or of a periodicallyclosed contact, the electromagnet may be replaced by the improved deviceforming the object of the invention. This change permits reduction ofthe consumption of electricity and avoidance of 3 is notched and magnetsactually employe rapid deterioration of the contact. Further, practiceshows that with this device a. batte operating with a single element of1" is su cient to obtain rewindin With electro- (5 which do not employ apermanent magnet, it is necessary to use batteries of higher voltages.-

There is shown by way of example in Figures 12, 13 and 14, an improvedconstruction for an electrically wound clock or watch comprising theelectro-magnet forming the obect of the invention.

The time mechanism shown in the u per comprises a ratchet w eel part ofFigure 12 R; which tends to rotate under the action of the pawl arm 1and of the driving spring 2. f

ThlS arm returns abruptly backwards from time to time under the actionof the electromagnet so as to assure continuity of the rotation of theratchet wheel R in the direction of f This wheel controls the gear chainof the clock and of the watch with the speed of the gearing beingregulated by an escapement and a balance wheel. (The principle itself ofthis rewinding system is well known).

The automatic switch which supplies the electro-magnet at the right timeis shown separately in Fi re 14 which consists of a part 3 stamped inthin silicon sheet metal. Any other magnetic product may be employedpossessing very weak hysteresis. This part is movable about the axis 0and is disposed adjacent to the pillars P and P or the pillars P and Por adjacent the extensions of these pillars P and P It is sufiicient forthese extensions P a and P to be strongly magnetized.

The part 3 is of the shape shown in Figure 14, the arcs 8 Z 8 t 8 t and8 t are of spiral sections so that the rotation of the part causes achan e in the reluctance of the magnetic circuit. 5n the other hand thepart provided with fittings preferably shaped as washers, of which one 4is of insulating material and the other 5 is of non-oxidizing conductinmetal. Between these fittings is a conducting pin 6 fast to the movablecoil of the electro-magnet. The di-' ameter of the pin 6 is less thanthe separation of the fittings 4 and 5.

In the position shown in full lines Figure 14 the part 3 is in unstableequilibrium. In effect this part tends to place itself in the magneticfield so as to reduce the reluctance of the magnetic circuit.Consequently, this part tends to rock to left and to right, the parts ofthe greatest radius tending to approach the magnetized pillars P a andP'..

The parts 3 and the pin 6 are interposed in the electric circuit asshown in Figure 13. One of the ends of the coil B is connected to one ofthe terminals of the battery, the other end is connected to the pin 6fixed on a support 7 electrically insulated on the frame of the coil(Figure 12).

. The movable art 3 of the switch ivots on the support w ich is notshown in Figure 12 (for the sake of cleamess). It is connected throughthe intermediar of a. ve flexible small spiral spring 8 to t e otherterminal of the batte V he movement 0 the pawl arm 1 is transmitted tothe coil of the electro-magnet ow-' mg to the pm 9 and to the fork 10solid with the arm 1.

The operation is as follows: (See Figures 12 and 13).

Between the winding actions, the movement of the mechanism is producedby the spring 2. The arm 1 rotates in the direction 1 and the coilrotates in the direction The shape of the pole pieces B and 2 of theelectro-magnet must be that of Figures 6 or 10 so that the magneticattraction of the magnet does not interfere in any way with the movementof the time mechanism. The pin 6 bears on the insulating part 4 and thecurrent is interrupted. When the pin 6 solid with the movable coilreaches the position of unstable equilibrium shown in Figure 14, thecontact piece 3 rotates suddenly in the direction f and takes up theposition indicated in dotted lines in Figure 14.

The conductin pin 6 comes into contact with the conducting fitting 5.The current passes through the coil as indicated in Figure 13.

The coil of the electro-magnet is then displaced suddenly in theopposite direction f and the pawl arm 1 returns back and cooks thedriving spring 2.

But at the end of its travel the pin 6 rotates the contact piece 3, andthe fitting 5 suddenly leaves the pin 6 so that the circuit isinterrupted. The parts then occupy the position shown in Figure 12, andthe operation is repeated.

In this device the abrupt displacement of the movable part of the switchis obtained by avoiding the sprin mechanisms which are usually employedring which have the disadvantage of acting with considerable frictionand of becoming out of order eventually owing to wear of the rubbingparts and jammmg.

The invention may be applied to time receivers in which the advance ofthe hands is controlled by spaced impulses sent out by a master clock.

The electro-magnet forming the object of the invention is particularlysuitable for time receivers operating by means of impulses ofalternating directions, in which an endeavour is made to reduce theoverall dimensions. This result is particularly desirable to obtain inthe case of hand controlling mechanisms which are placed behind translucent dials lit from behind by means of electric lamps. Theconstruction of such clocks may be simplified by fixing the mechanism itis then necessary to reduce to the. limit the dimensions of t emechanism, so that the shadow which it produces on the centre of thedial does not adversely affect the visibility of the hands.

Figures 15 and 6 show by way of example how the invention may be appliedto the construction of such a time mechanism. The frame of the coil isprovided with a control finger 11 which engages in the fork arm 12 solidwith the support 13 on which are articulated pawls 14 and 15 acting onthe ratchet wheel 16. It is advantageous to adopt pole pieces of suchsha' s that that armature of the coil tends to be inclined to left or tori ht, as has been explained with reference to igure 8.

After each emission of current, the coil remains in place and themagnetic attractions which prevail cause one or other of the pawls 14 or15 to bear on the locking sto s 16 and 17. Thus the hands are maintainein lace. Owing to the arrangement shown in 1 are 16, a ratchet wheel 16may be emplo ed aving a relatively large diameter an all the members maybe grouped in a very reduced area corresponding to the external shape ofthe magnet.

Various modifications may be made in the mechanism described within thespirit of the invention. In particular, instead of the permanent magnet,an electro-magnet ma be employed having a winding energized y acontinuous or rectified current.

The special shape of the pole pieces which enable the magneticattraction to be varied with the position of the movable parts accordingto a selected law can be applied to other types of polarizedelectro-magnets, and in particular to those which comprise a movablesoft iron armature polarized by a permanent magnet, and displaced in reation to other iron parts which are temporarily magnetized, owing tocoils of electric wire traversed by intermittent currents.

What I claim is 1. Polarized electro-magnet comprising a movablearmature carrying an energizing coil provided with polar enlargementsconsisting of stamped and bent ieces of sheet metal of high permeabilityand low hysteresis, which armature oscillates in a field of a permanentmagnet whose pole pieces consist of cylindrical iron illars connected tothe polar extremities o the ma et by concave sheet metal plates heldresillently between the polar extremities of the magnet and the pillars,and whose concavity is sufficient to accommodate the connections of thecoil.

2. Electro-magnet according to claim 1, in which the movable armatureconsists of two thin plates which are non-magnetic and carry the pivotsconnected by cross bars, on which the pole pieces of the coil arefitted, these parts having apertures for the passa e of the ends of thecore of the coil, assemb y being obtained b means of nuts screwedexternall on the en s of the core, this armature osci latgng in thefield of the permanent magnet.-

olarized electro-magnet according to claim 1, in which the polarenlargements of the armature are shaped as cylindrical surfaces havingas axis the axis of rotation of the coil and limited to an arc of smalllength relatively to the spacing of two adjacent polar 1pillars ofdiflerent polarity.

4. olarized electro-magnet according to claim 1, in which the polarenlargements of the armature are shaped as cylindrical surfaces havingas axis the axis of rotation of the coil and extending for an arc ofconsiderable length and, in the position of equilibrium of the coilprojecting considerably on either side of those of their points whichare nearest to the polar pillars.

5. Polarized electro-magnet according to claim 1, in which the polarenlargements of the armature are shaped as surfaces comprising at thecentre a cylindrical part having as axls the axis of rotation of thecoil limited to an arc of small length relatively to the space betweentwo adjacent olar pillars of different olarity, connected to cylindricalsurfaces 0 much smaller radius which in the position of equilibrium ofthe coil project considerably on either eide of those of their pointswhich are nearest to the polar pillars.

6. Device according to claim 1, in which several identical ermanentmagnets are disposed side by si e and in which the coil is given alength in the direction of its axis of rotation corresponding to thenumber of magnets employed.

In testimony whereof I have aflixed my signature.

MARIUS LAVET.

